1. Field of the Invention
This invention relates to disk drives and methods for generating signals marking the start of data sectors in a headerless disk drive architecture.
2. Description of Related Art
A conventional magnetic media for a hard drive is a disk having major surfaces divided into concentric tracks for data storage. Servo wedges subdivide the tracks into data frames where the portion of a servo wedge within a track is referred to as a servo sector and separates one data frame in the track from another. Each servo sector in a track contains information that a servo sequencer uses to keep a data head following the track. Servo wedges are typically spaced about the disk in a spoke-like pattern, and the time interval between a data head passing consecutive servo wedges depends on the angular velocity of the disk and is independent of the track being followed. Thus, a system clock signal that has the same frequency for all tracks controls timing when handling servo sectors or generating end-of-servo (EOS) pulses marking the ends of servo sectors and the starts of data frames.
For constant density recording in the data frames, the disk area per bit of data is constant, but the rate at which a data head encounters the data varies according to velocity of the track being followed. Accordingly, the data rate depends on the radius of the track, and a byte clock signal having a frequency that depends on the track being followed controls timing of data read or written. The data within the data frames is typically organized into data sectors, each of which contains the same amount of data, for example, 512 bytes. The data sectors may include a single data field that is entirely within a data frame or multiple data fields that are separated from each other, for example, by a servo sector. When reading or writing a data sector, the location of each data field (i.e. the start and splits in each data sector) need to be identified. One method for locating data fields uses information from a header of a data sector to locate splits in the data sector. However, split information stored in headers wastes disk space that could otherwise store data.
A headerless data sector format lacks headers containing split information and leaves more disk area for data storage. However, the disk controller requires split information from a source other than a header. Such split information can be stored in non-volatile memory or on disk in data sectors and then transferred to a data buffer memory. The split information can be stored more compactly in data sectors rather than in headers because the split information for one data frame often also applies to multiple data frames on multiple tracks. Handling the split information commonly requires additional data buffer capacity for the split information, additional bandwidth for split information data flow, and processing power to select and interpret the split information. An efficient format for split information and an efficient process for handling split information to minimize consumption of processing power is desired.